1. Field of the Invention
The present invention relates to an apparatus for judging the deterioration of a battery, and in particular, to an apparatus for judging whether the battery, especially for a vehicle, is deteriorating or not.
This application is based on Japanese Patent Application No. Hei 11-20793, the contents of which are incorporated herein by reference.
2. Description of the Related Art
In recent years, electric vehicles and hybrid vehicles have been developed in order to reduce the discharge of carbon dioxide, in consideration of the global warming effect. These vehicles have a motor which does not discharge any gas, and a battery for supplying electric energy.
The electric vehicle is continuously driven by the motor. The hybrid vehicle utilizes the motor to assist the engine, and is often driven only by the motor.
Accurately detecting the remaining charge in the battery that supplies energy to the vehicle is important for determining whether to start charging or not, and to detect the remaining available time and the life of the battery.
FIGS. 13A and 13B are diagrams for explaining the deterioration of a battery.
FIG. 13A shows the initial capacity of the battery, and the hatched area represents the capacity. As the battery deteriorates, the capacity of the battery decreases as shown in FIG. 13B, and therefore the maximum chargeable energy decreases even when the battery is charged for many hours.
A method for judging the deterioration of the battery based on a comparison with the maximum chargeable capacity is proposed. In this method, the battery is fully charged by a charger, and the charging current is integrated so that remaining charge in the full charge state is calculated. This remaining charge in the full charge state is divided by the initial remaining charge. When the obtained value is below a predetermined value, it is judged that the battery has deteriorated. The details of this method for judging the battery deterioration are disclosed in, for example, Japanese Patent Application, Unexamined First Publication No. Hei 5-284607.
Generally, the batteries on hybrid vehicles are not charged by external chargers (commercial electric power sources), and are charged by electric power generation by a regenerative brake when the vehicles decelerate. Therefore, the battery cannot be fully charged, and the judging of the battery deterioration by the above method may be inaccurate.
Further, a conventional method detects the remaining charge in the battery by time-integrating a charging current to the battery and a discharging current from the battery to the motor. The remaining charge basically corresponds to the total of charge stored in the battery. The total of the supplied and released electrical charge can be calculated by the time-integration of the electric current value (the charging current is positive, and the discharging current is negative). The details of this method can be understood from Japanese Patent Application, First Publication No. Hei 63-208773.
In general, the conventional electric current detector necessarily incurs an error. When the electric current is momentarily measured, the error may be permissible. However, in the time-integration of the electric current, the errors are also integrated so that the discrepancy increases as time passes. This discrepancy is not permissible in the time integration because it reduces the detection accuracy. Therefore, when the battery deterioration is judged based on this time integration value which includes the permissible errors, the accuracy in the judgement may be insufficient.
Further, the batteries on hybrid vehicles are charged not by the external chargers but by the regenerated current, that is, the current generated by the motor rotated by the engine. Therefore, the battery on the hybrid vehicle may not be fully charged, and the method disclosed in Japanese Patent Application, First Publication No. Hei 63-208773, cannot accurately judge the deterioration of the battery.
It is therefore an object of the present invention to provide an apparatus for judging of deterioration of a battery, which can accurately judge the deterioration of the battery even when the battery is frequently and transiently used.
In order to accomplish the above object, the apparatus for judging of deterioration of a battery, comprises: a current detector (30, 40) for detecting output electric current from and regenerative electric current to the battery; a voltage detector (44) for detecting a voltage output from the battery; an integrator (54) for calculating the remaining charge in the battery by integrating the result of detection by the current detector; a threshold voltage calculator (56) for calculating threshold voltage values corresponding to first and second specified values of the remaining charge, based on the electric current value filtered by the filter; a comparator (58) for comparing the threshold voltage value, calculated by the threshold voltage calculator, with the output voltage value from the battery; a corrector (60) for correcting the remaining charge to the first or second specified value when the output voltage value has reached the threshold voltage value; a current integrator (54, S612) for integrating the output current from the battery and the regenerative current after the remaining charge was corrected to the first specified value until the remaining charge is corrected to the second specified value; and a deterioration judgement device (62) for judging the deterioration of the battery when the value obtained from the integration by the current integrator is equal to or below a predetermined deterioration criterion.
In this invention, the current integrator integrates the output current from the battery and the regenerative current after the remaining charge was corrected to the first specified value until the remaining charge is corrected to the second specified value. The deterioration judgement device judges the deterioration of the battery when the value obtained from the integration by the current integrator is equal to or below a predetermined deterioration criterion. Therefore, the accuracy in the judgement is improved.
In another aspect of the invention, the apparatus further comprises: a temperature detector (42) for detecting the temperature of the battery; and a battery deterioration judgement prohibition device (64) for prohibiting the judgement of the deterioration of the battery when the temperature detected by the temperature detector is below a preset temperature, when the time for the integration by the current integrator is longer than a predetermined time, or when the charging/discharging current is above a charging/discharging threshold value.
Even when the battery temperature is low, when the charging/discharging current is high, or when the measured time is long, mis-judgements can be avoided.